An early chemical amplification positive resist composition composed of a photo-acid generator and a resin protected by an acid-decomposable group is disclosed, for example, in U.S. Pat. No. 4,491,628. This chemical amplification positive resist composition is a pattern forming material of forming a pattern on a substrate by producing an acid in the exposed area upon irradiation with radiation such as far ultraviolet light and through a reaction using the acid as a catalyst, changing the developer solubility of the area irradiated with actinic radiation and that of the non-irradiated area.
Various positive resist compositions containing a resin protected by an acid-decomposable group have been heretofore known, and for example, JP-A-5-249682 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a resist composition using a polyhydroxystyrene resin protected by an alkoxy (acetal) group, JP-A-9-211866 discloses a resist composition using a polyhydroxystyrene resin protected by two different acid-decomposable groups, JP-A-2000-352822 discloses a resist composition using a resin protected by an acetal group having a heterocyclic group at the terminal through a linking group, JP-A-2002-49156 discloses a resist composition using a polyhydroxystyrene resin protected by two different acetal groups, and JP-A-2004-246326 discloses a resist composition using a polyhydroxystyrene resin protected by an acid-decomposable group containing a group (heterocycle) having absorption at 248 nm.
However, when a high-reflection substrate is used directly without an antireflection film as in the case of forming a pattern for implantation involving ion injection or the like, a general positive resist composition causes an increase in the swing amplitude or production of a strong standing wave. In this respect, improvements are demanded. It is also required to improve the performance in terms of resolution and film loss.